Method and device for determining the torque on gear shafts

ABSTRACT

A method and a device for determining the torques on gear shafts. With the help of this method and the device in the case of a constant transmission ratio, the rotational speed of a first gear shaft ( 2, 19 ) and the rotational speed of a second gear shaft ( 3, 22 ) are measured cyclically. A first torque is present on the first gear shaft and a second torque is present at the second gear shaft. The second gear shaft is driven by the first gear shaft directly or indirectly, via gears ( 5, 6, 7, 8; 20, 21 ). A quotient is computed from these two rotational speeds, and stored so the current quotient can be compared with the quotient of the previous measuring cycle. In the case of a difference in the quotients of the current and the previous measurement, a change in the torque of the first gear shaft can be assumed.

This application is a national stage completion of PCT/EP2004/010295filed Sep. 15, 2004 which claims priority from German Application SerialNo. 103 47 494.3 filed Oct. 13, 2003.

FIELD OF THE INVENTION

The invention concerns a method and a device for determining torque ongear shafts.

BACKGROUND OF THE INVENTION

It is well known among transmission experts that in order to optimizedrive strategies and gear change operations of automated manualtransmissions, the information of the current motor or gear input torqueis needed. In practice, the current torque is measured by taking thecrankshaft or gear input shaft rotational speeds as well as theaccelerator pedal position into consideration, which allow the presenttorque on the crankshaft and/or on the gear input shaft to be determinedwith the help of a characteristic torque curve that is stored in anevaluation and control unit.

In case of retarders, i.e., wear free service brakes of the vehicle,according to the state of the art, their braking torque is determined asa function of the braking pressure and a characteristic curve which isalso recorded in a control and regulating unit. Good regulation of thebraking effect of retarders, however, is not quite possible based onsuch a measurement of the braking effect.

Starting from this state of the art, the object of the invention is todevelop a method and a device with the help of which the change in inputtorque of a transmission or the braking torque on a retarder can bedetermined easily and quickly.

SUMMARY OF THE INVENTION

The invention is based on the knowledge that in the case of a constantgear transmission ratio and constant input torque, the rotational speedof a transmission input shaft and a transmission output shaft have afixed ratio to each other. If this ratio changes, it indicates a changein the gear input torque in the case of a constant transmission ratio.This changed value could be used to determine the transmission inputtorque.

Having knowledge of this context, an innovative method has beensuggested in which for a constant transmission ratio the rotationalspeeds of a first gear shaft and a second gear shaft can be cyclicallymeasured, wherein a first torque is present at the first gear shaft anda second torque is present at the second gear shaft and the second gearshaft is driven by the first gear shaft directly or indirectly throughgears. In addition, a quotient is derived from these two rotationalspeeds and is subsequently recorded so that the current quotient can becompared to the previous quotient measured and a difference in the valuebetween the current measurement and the previous measurement canindicate a change in the torque of the first gear shaft.

This changed value alone could be used for controlling and regulatingthe transmission ratio changing operations in a transmission. Accordingto a preferred embodiment of the invention, it is provided that theinput torque in the transmission be determined from the difference inthe quotients.

In another embodiment of the invention, it is provided that therotational speeds of both gear shafts are determined with the help ofsensors, which generate electric impulses as a function of therotational speed. From the measured electric impulses of the rotationalspeed sensors on both gear shafts, in the case of a constanttransmission ratio, a phase or angle shift of the impulses can bedetermined from a change in torque, which shift is proportional to thetransmitted torque and to the elasticity of the components transmittingthe torque, and also be evaluated as a characteristic for the inputtorque.

Although this method is preferably used to determine the torque of acombustion engine, even other applications in transmissions could bemeaningful. The braking torque of a retarder could be similarlydetermined, and this value could be used for controlling and regulatingthe same.

If the torque of a drive unit, such as a combustion engine, for example,needs to be determined, the inventive device offers the possibility ofutilizing the rotational speed of the drive motor or the gear inputshaft (first gear shaft) as well as the rotational speed of a gear driveshaft (second gear shaft) for determining the described torque or changein torque.

If the braking torque of a retarder needs to be determined, therotational speeds of two gear shafts associated with a retarder aremeasured in a similar way.

In addition, the above method can be used to determine the tractiontorque and shearing torque in a transmission.

Finally, it should be pointed out that the inventive method can be usedalone or together with one or more embodiments or further developmentsdetermining the torque in automatic or automated manual transmissionswith or without a splitter drive.

A device for determining the torque on the gear shafts comprises anevaluation and control device, which captures and analyzes torquerelevant measurement signals on the transmission with the help ofsensors via sensor lines. It is provided that the evaluation and controldevice is connected to two rotational speed sensors, which are arrangedon two gear shafts, wherein a first torque is present at the first gearshaft and a second torque is present at the second gear shaft.

For the analysis of the captured measurements, the evaluation andcontrol device comprises a computation area where a rotational speedquotient is determined from the captured rotational speed measurementsof a measuring cycle. In addition, a data storage device is alsoprovided for storing the rotational speed measurements and/or therotational speed quotients. In addition, the evaluation and controldevice comprises an area for comparison, which allows a comparison ofthe quotient of the latest measuring cycle to the quotients of theprevious measuring cycle. Apart from this, the evaluation and controldevice comprises a decision area in which the change in torque isdetermined on the basis of the quotient comparison.

Finally, it is considered advantageous to have a determination area inthe evaluation and control device, in which area the first torquepresent on the one gear shaft (input torque) can be determined from thechange in the torque.

On the basis of the determined information, the evaluation and controldevice can finally trigger control orders for executing the gear ratiochange operation in the transmission.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described, by way of example, with referenceto the accompanying drawings in which:

FIG. 1 is a countershaft transmission with a measuring system fordetermining the gear input torque;

FIG. 2 is a sensor gear for a rotational speed sensor at the gear inputshaft;

FIG. 3 is a sensor gear for a rotational speed sensor at the gear outputshaft;

FIG. 4 is a diagram illustrating the dependence of an input torque Mefrom a phase or angle shift α, and

FIG. 5 is a secondary retarder with two rotational speed sensors.

DETAILED DESCRIPTION OF THE INVENTION

According to this, the method can be used in a countershaft transmission1 of the type shown in FIG. 1, in which a gear input shaft 2 and a gearoutput shaft 3 are disposed co-axially to each other in a transmissionhousing. Axially parallel to both these shafts, a lay shaft 4 isdisposed in the transmission, a drive gear 6 of which can be driven byan output gear 5 on the gear input shaft 2.

In addition, rigid gears 7 are arranged on the lay shaft 4, which meshwith idler gears 8 for implementing specific forward gear transmissionratios. The idler gears 8 are arranged on the gear output shaft 3 andcan rotate on the shaft. For the purpose of alternately slowing down andnon-rotatably connecting the idler gears 8 with the gear output shaft 3,synchronization and coupling devices 9 arranged on the output shaft,which are mounted axially displaceably and non-rotatably.

For the determination of a change in the input torque present on thegear input shaft 2, a device is arranged on the transmission 1, which isassociated with an evaluation and control device 14 which, in thesimplest case, is identical to the control and regulating device of thetransmission. This evaluation and control device 14 is connected torotational speed sensors 12, 13 via sensor lines 15, 16 as well as viacontrol lines 17 to actuators, which are not shown here. The latteralternately actuate sliding sleeves of the synchronization and couplingdevices 9, in the known fashion, which sleeves can be axially displacedon the gear output shaft 3, but are mounted non-rotatably.

As shown in FIGS. 2 and 3, the rotational speed sensors 12, 13 work inconjunction with rotational speed sensing gears 10, 11, which aremounted non-rotably on the gear input shaft 2 and gear output shaft 3,respectively. The teeth of these rotational speed sensing gears 10, 11generate the same electric impulses on passing the sensors 12, 13, whichare fed to the evaluation and control device 14 as described.

In the case of constant gear ratios, the rotational speed of the inputgear shaft 2 and the rotational speed of the gear output shaft 3 have aconstant ratio with respect to each other. This ratio (the quotient ofthe gear input shaft rotational speed and the gear output shaftrotational speed) is determined by the evaluation and control device 14and stored. Subsequently, the rotational speed of the gear input shaft 2and that of the gear output shaft 3 are determined in a next measuringcycle, and a second quotient is determined from these values. If adeviation is found between the current quotient and the previousquotient during the subsequent comparison, it would imply that the gearinput torque has changed.

Since in the case of manual transmissions, the gear input shaft isgenerally connected to the output shaft of a driving motor, for exampleto the crankshaft, of a combustion engine without influencing the torqueto be transmitted. The determined change in the input torque can beinterpreted as a change in the torque of the combustion engine.

This change of the input torque is reflected in the measurement signalcourse of the sensors 12, 13 at the gear shafts 2, 3, as shown in theFIGS. 2 and 3, in that a phase or an angle shift a of the measuredsignals can be determined, which is proportional to the torquetransmitted by the gearbox and also dependent on the elasticity of thetransmission components transmitting the torque.

With the knowledge of a starting torque for the described measurementsand with the help of the phase or the angle shift a and/or the quotientcomparison obtained as described earlier, the change in the input torqueand the current input torque Me can be computed. This is explained inFIG. 4 by way of example with the help of a characteristic curve 26.

Apart from determining the engine torque or the transmission inputtorque, the above method and the associated device enable thedetermination of the current braking torque of a retarder. Such aretarder 18 is illustrated schematically by way of example in FIG. 5,being a so-called secondary retarder in this case.

In the case of this retarder 18, a gear output shaft 19 carries a rigidgear 20, which meshes with a rigid gear 21 on a retarder shaft 22. Thelatter shaft 22 carries a rotor 23 of a hydrodynamic braking device inthe known manner, which device works together with an associated stator24 from a fluidic point of view.

For the determination of the braking moment generated by the retarder18, rotational speed sensor gears 27, 28 are attached to thetransmission output shaft 19 and the retarder shaft 22, which worktogether with rotational speed sensors 25, 29. These rotational speedsensors 25, 29, as is shown in FIG. 1, are connected to the evaluationand control device 14 through sensor lines 15, 16. The analysis of themeasurements of the rotational speed sensors 25, 29 is carried out inthis device.

With the help of such a design, it is possible to determine the brakingeffect on the transmission output shaft 19 with the help of the retarder18 and use it for controlling the braking power. This is carried outthrough targeted filling of the oil space between the rotor 23 and thestator 24 of the retarder 18.

REFERENCE NUMERALS

-   1 countershaft transmission-   2 gear input shaft-   3 gear output shaft-   4 lay shaft-   5 output gear-   6 drive gear-   7 rigid gear-   8 idler gear-   9 synchronization and coupling means-   10 rotational speed sensor gear-   11 rotational speed sensor gear-   12 rotational speed sensor-   13 rotational speed sensor-   14 evaluation and control device-   15 sensor line-   16 sensor line-   17 control line-   18 secondary retarder-   19 transmission output shaft-   20 rigid gear on the transmission output shaft-   21 rigid gear on the retarder shaft-   22 retarder shaft-   23 rotor of the retarder-   24 stator of the retarder-   25 rotational speed sensor on the retarder shaft-   26 function curve Me=f(α)-   27 rotational speed sensor gear-   28 rotational speed sensor gear-   29 rotational speed sensor-   Me input torque-   α phase or angle change

1. A method for determining the torque on transmission shafts, themethod comprising the steps of: cyclically measuring a rotational speedof a first gear shaft (2, 19) and a rotational speed of a second gearshaft (3, 22) of transmission with a constant transmission ratio, afirst torque being present on the first gear shaft (2, 19) and a secondtorque being present on the second gear shaft (3, 22), and the secondgear shaft (3, 22) being driven one of directly and indirectly by thefirst gear shaft (2, 19) via at least a two gears (5, 6, 7, 8; 20, 21);computing a value from the rotational speed of the first gear shaft (2,19) and the rotational speed of the second gear shaft (3, 22) andstoring the computed value; comparing a current value with a value of aprevious value; deriving a change in the torque of the first gear shaft(2, 19) by a difference between the current value and the previousvalue; determining the rotational speeds of the two gear shafts (2, 3;19, 22) by rotational speed sensors (12, 13; 25, 29), which generatespeed-related electrical impulses; and determining one of a phase orangle shift (α) from measured electric impulses of the rotational speedsensors (12, 13; 25, 29) on the two gear shafts (2, 3; 19, 22), which isproportional to transmitted torque and to elasticity oftorque-transmitting components of the transmission and is also acharacteristic of input torque.
 2. The method according to claim 1,further comprising the step of measuring rotational speeds of one of adriving motor, a gear input shaft (2) and a rotational speed of a gearoutput shaft (3).
 3. The method according to claim 2, further comprisingthe step of determining a torque of a combustion engine.
 4. The methodaccording to claim 1, further comprising the step of using a quotientfrom the two rotational speeds as the value computed from the tworotational speeds.
 5. The method according to claim 1, furthercomprising the step of determining one of a traction and a shearingtorque in the transmission.
 6. The method according to claim 1, furthercomprising the step of using the quotient for determining torque in oneof an automatic or automated manual transmission with at least onesplitter drive.
 7. The method according to claim 1, further comprisingthe step of using the quotient for determining torque in one of anautomatic or automated manual transmission without any splitter drive.8. A method for determining the torque on transmission shafts, themethod comprising the steps of: cyclically measuring a rotational speedof a first gear shaft (2, 19) and a rotational speed of a second gearshaft (3, 22) in a transmission with a constant transmission ratio, afirst torque being present on the first gear shaft (2, 19) and a secondtorque being present on the second gear shaft (3, 22), and the secondgear shaft (3, 22) being driven one of directly and indirectly by thefirst gear shaft (2, 19) via at least two gears (5, 6, 7, 8; 20, 21);computing a value from the rotational speed of the first gear shaft (2,19) and the rotational speed of the second gear shaft (3, 22) andstoring the computed value; comparing a current value with a value of aprevious value; deriving a change in the torque of the first gear shaft(2, 19) by a difference between the current value and the previousvalue; determining the rotational speeds of the two gear shafts (2, 3;19, 22) via rotational speed sensors (12, 13; 25, 29), which generatespeed-related electrical impulses; and measuring rotational speeds oftwo shafts (19, 22) associated with a retarder (18) and determining abraking torque of a retarder (18).